1. Field of the Invention
This invention relates to digital logic circuits and, more particularly, to techniques for making digital logic circuits insensitive to spurious input signals and ground spikes on, for example, signal lines for interrupt signals.
2. Prior Art
The feature sizes of the devices on semiconductor integrated circuits are becoming increasingly smaller so that integrated-circuit dies are much more densely packed. The various devices are much closer to each other and signal lines are laid out with much closer spacings. The frequency of operation of these more densely packed integrated circuits are also increasing. The result is that integrated circuits are operating with increased internal crosstalk and with more cross coupled electronic noise.
Attempts to moderate this problem have been made by reducing noise pickup on signal and power buses by use of various I/O and bussing designs. Reduction of internal crosstalk noise in a densely packed integrated circuits has not been effectively addressed. For example, in a 32-bit bus system where the tri-state bus driver circuits are latched into a high-impedance state, the bus driver circuits are particularly susceptible to crosstalk pickup because of their high impedance state. As another example, each of two signal lines adjacent to a third signal line may have signals going in opposite directions. The third signal line may pickup signals from both of the adjacent signal lines such that the signal on the third signal line appears to be delayed.
The need has arisen for a technique to discriminate against unwanted noise bursts and crosstalk signal pulses within an integrated circuit, and, in particular, on interrupt signal lines for a microcomputer.